Muscle contraction Flashcards
What are skeletal muscles?
A type of muscle that you use to move
What do tendons do?
Attach skeletal muscle to bones
What do ligaments do?
Attach bone to bone
What is an antagonistic pair?
2 muscles that work together to move a bone
What is the agonist?
The muscle that contracts
What is the antagonist?
The muscle that relaxes
What do neurones stimulate muscles to do?
Contract
What are skeletal muscles made from?
Muscle fibres
What are muscle fibres?
Large bundles of cells that make up skeletal muscle
What is the sarcolemma?
The cell membrane of muscle fibres
What are transverse tubules?
Bits of the sarcolemma that fold inwards across the muscle fibre and stick into the sarcoplasm
What do transverse tubules do?
Help to spread electrical impulses throughout the sarcoplasm so they reach all over
What is the sarcoplasmic reticulum?
A network of internal membranes that runes through the sarcoplasm
What does the sarcoplasmic reticulum do?
Stores and releases calcium ions that are needed for muscle contraction
Name 2 features of skeletal muscle
Lots of mitochondria to provide ATP
Multinucleate
What are myofibrils?
Long cylindrical organelles that make up muscle fibres
What do myofibrils do?
Specialised for contraction
What do myofibrils contain?
Bundles of thick and thin myofilaments that move past each other to make muscles contract
What are thick myofilaments made from?
Myosin
What are thin myofilaments made from?
Actin
What do A bands contain?
Thick myosin filaments and some overlapping thin actin filaments
What do I bands contain?
Only thin actin filaments
What does the H zone contain?
Only myosin filaments
What is the Z line?
End of each sarcomere
What is the M line?
Middle of myosin filaments
What are sarcomeres?
Short units that make up myofibrils
Explain the sliding filament theory
Myosin and actin filaments slide over one another to make the sarcomeres contract. The simultaneous contraction of lots of sarcomeres means the myofibrils and muscle fibres contract.
What happens to the sarcomere as it contracts?
It gets shorter
What do myosin filaments contain?
Globular heads
What do the globular heads do?
Are hinged so move back and forth
Describe the structure of a myosin head
They have a binding site for actin and a binding site for ATP
What do actin filaments contain?
Binding sites for myosin heads called actin myosin binding sites
Where is tropomyosin found?
Between actin filaments
What does tropomyosin do?
Helps myofilaments move past each other
Explain the role of tropomyosin in resting muscles
Blocks the actin myosin binding site. This means that myofilaments can’t slide past each other because the myosin heads can’t bind to the actin myosin binding sites on the actin filaments
What does an action potential from a motor neurone do to a muscle?
Stimulates the muscles cells
Depolarises the sarcolemma
Where does the depolarisation spread to?
Down the T tubules to the sarcoplasmic reticulum
What does the depolarisation cause?
The sarcoplasmic reticulum to release stored calcium ions into the reticulum
What do the calcium ions do in muscle contraction?
Bind to a protein attached to tropomyosin causing the protein to change shape. This pulls the attached tropomyosin out of the actin myosin binding sites in the actin filament. This exposes the binding site which allows the myosin head to bond.
They also activate ATP hydrolase which hydrolyses ATP to provide the energy needed for muscle contraction.
What is an actin myosin cross bridge?
The bond that is formed when a myosin head binds to an actin filament
What does the energy released from ATP do in muscle contraction?
ATP causes the myosin head to bend which pulls the actin filament along in a rowing action .
It also provides the energy to break the actin myosin cross bridges so the myosin head detaches from the actin filament after it is moved.
What happens after the myosin head detaches?
The myosin head reattaches to a different binding site further along the actin filament. A new actin myosin cross bridge is formed and the cycle is repeated.
What causes the muscle to contract?
Cross bridges form and break rapidly pulling the actin filament along which shortens the sarcomere
What needs to be present for the cycle of muscle contraction to be present?
Calcium ions
What happens during muscle relaxation?
- When the muscle stops being stimulated, calcium ions leave their binding sites and are moved by active transport back into the sarcoplasmic reticulum.
- This causes the tropomyosin molecules to move back so they can block the actin myosin binding sites again.
- Muscles are not contracted as no myosin heads are attached to actin filaments.
- The actin filaments slide back to their relaxed position which lengthens the sarcomeres
Name the 3 methods of ATP resynthesis
Aerobic respiration
Anaerobic respiration
ATP-PC system
Explain aerobic respiration
Most ATP is generated via oxidative phosphorylation in the cell’s mitochondria.
It only works when there is oxygen so it is good for long periods of low intensity exercise
Explain anaerobic respiration
ATP is made rapidly by glycolysis
The end product is pyruvate and is converted to lactase by lactate fermentation
Lactate can quickly build up in the muscles and cause muscle fatigue
Anaerobic respiration is good for short periods of high exercise
Explain the ATP-PC system
ATP is made by phosphorylating ADP
PC is stored inside cells and the ATP-PC system generates ATP very quickly
PC runs out after a few seconds so it is used during short bursts of vigorous exercise
The ATP-PC system is anaerobic and alactic
Describe slow twitch muscle fibres
- contract slowly
- muscles you use for posture
- good for endurance athletes
- can work for long periods of time without tiring
- energy’s released slowly through aerobic respiration. Lots of mitochondria and blood vessels supply the muscles with oxygen
- reddish in colour as they are rich in myoglobin
Describe fast twitch muscle fibres
- contract very quickly
- muscles you use for fast movement
- good for short bursts of speed and power
- get tired very quickly
- energy is released through anaerobic respiration using glycogen. There are few mitochondria or blood vessels
- white in colour
